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/diy/ - Do-It-Yourself


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>> No.2039073 [View]
File: 23 KB, 1208x670, in amp from op amps.png [View same] [iqdb] [saucenao] [google] [report]

what technology are you designing in? discrete TTL? discrete 4000 series CMOS? CPLD? FPGA? discrete NMOS?
>Any similar *well-documented* and simple chips to draw inspiration from?
these were used in some early MCU-based calculators http://bitsavers.informatik.uni-stuttgart.de/components/ti/TMS1000/TMS1000pgmRef_1975.pdf
these were used in things like microwave ovens and timers http://datasheets.chipdb.org/National/COP400/NS_COP400_Family.pdf
>How many registers do I use?
maybe none, maybe just one accumulator/working register and a condition code register
>How long to make the instructions (8-bit?)?
8-bit is a good size, there's room for a lot of of instructions with 4-bit immediate operands, but you might have to leave yourself room to do some tricks and you'll probably be bank-switching. also remember to deal with long jumps in your instruction encoding, including any skip instructions you might implement
>How many nibbles of RAM is enough for a basic 10-digit calculator?
far less than you can buy as a packaged component tod- oh, Jameco has those 74S189 fuckers NOS for $4 each. anyway. 64 nybbles would be ample, even extravagant. room enough for the display, a memory, a scratchpad, and to memory-map the keyboard
>How deep to make the function stack?
depends on how you structure your code and how big your program store is. 4 levels might be enough, 8 is more than enough. you'll find out for sure when you write the program

in amps don't have external feedback in usual configurations. they just figure the difference between the two inputs, gain it up by an application-specific but controlled multiple, and offset that by a reference input (picrel at R6). not the same thing as op amps
anyway op amps are a low impedance signal source because their output currents are relatively high and R=E/I

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